1. Field of the Invention
The present invention relates generally to a vibration damping device including an elastic body elastically connecting two mutually spaced-apart mounting members, which are interposed between two members of a vibration system and are attached at these two mounting members to respective two members of the vibration system so as to flexibly connect these two members or mount one of these members on the other member in a vibration damping manner. More particularly, the present invention is concerned with a vibration damping device which exhibits an improved durability of the elastic body without restricting an effective free length of the elastic body.
2. Description of the Related Art
As one type of a vibration damping device interposed between two members of a vibration system so as to flexibly connect these two members or mount one of these members on the other member in a vibration damping manner, there is know a vibration damping device as disclosed in U.S. Pat. No. 6,017,024, wherein a first metallic mounting member and a second cylindrical metallic mounting member having a cylindrical portion, which are attachable to the respective two members of the vibration system, are spaced apart from each other such that an open end portion of the cylindrical portion of the second mounting member is opposed to the first mounting member, and are elastically connected to each other by an elastic body interposed therebetween. More specifically, the elastic body is bonded at its central portion to the first mounting member and a its circumferential surface to the inner circumferential surface of the cylindrical portion of the second mounting member. The vibration damping device is favorably used as an engine mount of a motor vehicle, for example.
This type of the vibration damping device is likely to suffer from a problem of cracking or other defects which occurs at the circumferential portion of the elastic body, which is bonded to the inner circumferential surface of the open end portion of the second mounting member, resulting in deterioration of durability of the elastic body. As a method to cope with this problem, there is proposed to modify the vibration damping device such that the second mounting member is formed at the open end portion of its cylindrical portion with an outward flange in order to increase a bonding surface area of the elastic body contact with respect to second mounting member, or alternatively the second mounting member includes a tapered portion which has a diameter gradually increasing toward the open end portion of the second mounting member in order to ease stress-concentration on a local portion of the elastic body. However, the use of such an outward flange or a tapered portion formed in the open end portion of the second cylindrical mounting member inevitably leads to an increase only in the diameter of the one open end portion of the second cylindrical mounting member. Since a space for accommodating the vibration damping device is limited, the diameter of the cylindrical portion of the second mounting member other than the outward flange or the tapered portion of the second mounting member is accordingly restricted, resulting in undesirable decreases in an entire volume of the elastic body and decrease in a substantial effective free length of the elastic body, in other words, the length of the elastic body connecting the first and second mounting members. Thus, the use of the outward flange or the tapered portion may possibly result in adverse influence on a spring characteristic of the elastic body. In particular, the above-indicated outward flange and the tapered portion of the second mounting member are not employable in the case where the second mounting member is fixed in the bracket such that the open end portion of the second mounting is press-fitted in the fixing bore of the bracket.
In view of the above, there has been desired to provide a vibration damping device which assures an improved durability of the circumferential portion of the elastic body which is bonded to the inner circumferential surface of the open end of the second mounting member, without increasing the diameter of the open end of the second mounting member. To meet this requirement, it is considered to modify the vibration damping device such that the open end portion of the second mounting member extends axially outward direction, so that a circumferential fillet is provided at an edge of the circumferential portion of the elastic body such that the fillet extends from the edge axially outwardly along the inner circumferential surface of the axially outward extending portion of the second cylindrical mounting member, and is bonded to this inner circumferential surface. In this case, however, the second mounting member radially outwardly disposed on the elastic body protrudes axially outward from the circumferential portion of the large-diameter portion of the elastic body. This leads to difficulty in opening the mold for molding the elastic body in a direction perpendicular to an axial direction thereof. Therefore, a degree of freedom in arranging the configuration, structure, or the like of the elastic body is significantly decreased, due to the above-indicated restriction in construction of the mold for molding the elastic body.
For instance, when the mold for molding the elastic body consists of a pair of mold halves which are butted to each other in the axial direction thereof to define therebetween a mold cavity for forming the elastic body, the configuration of the elastic body is inevitably restricted such that the diameter of the elastic body is not smaller than that of the first mounting member. This makes it impossible to protrude the peripheral portion of the first mounting member in the direction perpendicular to the axial direction from a circumferential portion of the central portion of the elastic body which is bonded to the first mounting member. That is, it is impossible to provide a circumferential fillet in an edge of the circumferential portion of the central portion of the elastic body, which edge is bonded to the peripheral portion of the first mounting member, making it difficult to provide a structure like the circumferential fillet for easing stress-concentration to the bonding portion of the elastic body with respect to the peripheral portion of the first mounting member. This drawback may possibly lead to deterioration of the durability of the elastic body.
The present invention was developed in the light of the above situation. It is therefore an object of the present invention to provide a vibration damping device having a novel structure, which is compact in size without increase of a diameter of the second mounting member, and which is capable of providing a sufficiently large free length of the elastic body. The vibration damping device also ensures an excellent durability of the elastic body, by avoiding stress concentration on local portions of the elastic body at which the elastic body is bonded to the first and second mounting members.
The above object of the invention may be achieved according to the principle of the present invention, which provides a vibration damping device interposed between two members of a vibration system for elastically connecting these two members in a vibration damping manner, the vibration damping device comprising: (a) a first mounting member and a second mounting member including a cylindrical portion, which are spaced apart from each other such that an open end portion in one of axially opposite ends of the cylindrical portion of the second mounting member is opposed to the first mounting member, and which are attachable to the two members of the vibration systems, respectively; (b) an elastic body elastically connecting the first and second mounting member such that the elastic body is bonded at a central portion thereof to the first mounting member and at a peripheral portion thereof to an inner circumferential surface of the second mounting member; and (c) a constricted part being integrally formed in the open end portion of the cylindrical portion of the second mounting member such that the constricted part protrudes radially inwardly of the cylindrical portion and extends circumferentially over an entire circumference of the cylindrical portion, and that the constricted part has the maximum outer diameter thereof not larger than that of the cylindrical portion, the peripheral portion of the elastic body being bonded to respective inner circumferential surfaces of the constricted part and the cylindrical portion of the second mounting member so that the constricted part and the cylindrical portion are elastically connected to the first mounting member via the elastic body.
In the vibration damping device according to the present invention, the provision of the constricted part formed in the upper open end portion of the second mounting member permits an increase in area of a surface of the elastic body bonded to the upper open end portion of the second mounting member, and a decrease in degree of concentration of stress to the bonding surface of the elastic body with respect to the upper open end portion of the second mounting member, upon deformation of the elastic body. This arrangement results in an improved durability of the elastic body and the resultant increase of the durability of the vibration damping device.
In the present mode of the invention, the constricted part is formed only in the upper open end portion of the second mounting member where the elastic body is likely to suffer from problems of the stress-concentration and cracking or other defects, as well as the maximum outer diameter of the constricted part is made not larger than the outer diameter of the cylindrical portion of the second mounting member, so that the vibration damping device constructed according to the preset invention is made compact in size. Further, the elastic body is bonded not only to the constricted part but also to the cylindrical portion having the outside diameter larger than that of the constricted part. This arrangement is effective to obtain a sufficient volume of the entire of the elastic body and an effective free length of the elastic body, thereby ensuring a further improved durability of the elastic body and a high degree of freedom in selecting materials of the elastic body and in arranging spring characteristics of the elastic body. The cylindrical portion of the second mounting member may be open in one of axially opposite ends thereof, or alternatively may be open in both axially opposite ends thereof.
For improved efficiency and reduced cost of manufacture of the second mounting member, it is preferable that the second mounting member is made of metallic materials such as steel by pressing. For assuring the above-indicated technical advantages of the present invention, the cylindrical portion as well as the constricted part of the second mounting member need to be substantially elastically connected to the first mounting member via the elastic body interposed therebetween. That is, respective portions of the elastic body bonded to the inner surfaces of the constricted part and the cylindrical portion of the second mounting member are both required to extend directly from the respective inner surfaces toward the first mounting member in a generally diametrical direction so that both portions of the elastic body are effectively elastically deformed upon application of the vibrational load to the vibration damping device.
According to one preferred form of the invention, the elastic body includes a connecting portion adapted to connect the first and second mounting members and having a circumferential surface serving as a free surface. The free surface having a tapered cylindrical shape extending axially outwardly and radially inwardly from the open end portion of the constricted part of the second mounting member. The vibration damping device constricted according to this preferred form of the invention is capable of obtaining the effective free length of the elastic body in the connecting portion of the elastic body, while avoiding an increase in diameter of the second mounting member. Further, the present vibration damping device is capable of reducing a tensile stress generated in the elastic body when the first and second mounting members are moved toward each other in the axial direction due to an application of the vibrational load in the axial direction to the vibration damping device, resulting in a further improved durability of the elastic body and the vibration damping device. More preferably, the elastic body may be provided with a cavity open in a large-diameter end face thereof. In this arrangement, occurrence of the tensile stress in the elastic body due to the axial displacement of the first and second mounting members close to each other, is advantageously eliminated or reduced, resulting in a further improved durability of the elastic body or the vibration damping device.
In one advantageous form of the above preferred form of the invention, the elastic body has a small-diameter portion and is bonded at an end face of the small-diameter portion thereof to the first mounting member, while the first mounting member has a protruding portion protruding in a radially outward direction thereof from a peripheral portion of the end face of the small-diameter portion of the elastic body. The elastic body further including a circumferential filled formed in the peripheral portion of the end face of the small-diameter portion thereof so as to extend radially outwardly from the peripheral portion with a curved surface and so as to be bonded to the protruding portion of the first mounting member. In this arrangement, the stress-concentration on the peripheral portion of the end face of the small-diameter portion is advantageously reduced owing to the provision of the fillet, resulting in a further improved durability of the elastic body. In this preferred form of the invention, the elastic body has a tapered circumferential surface which extends axially outwardly and radially inwardly from the upper open end face of the second mounting member toward the first mounting member 12, permitting a use of a mold which is opened in a diametric direction thereof, in other words, which consists of a plurality of mold parts which are butted together at a parting plane extending in an axial direction of the mold, for forming an integral vulcanized product wherein the elastic body is bonded to the first and second mounting member in the vulcanization process of a rubber material for forming the elastic body in the mold. It is noted that the use of the mold which is opened in the diametric direction and which is simple in construction, may facilitate formation of the circumferential fillet provided in the bonding portion of the elastic body with respect to the first molding member, that is, the peripheral portion of the upper end face of the small-diameter portion of the elastic body.
According to another preferred form of the invention, the first mounting member includes an axially protruding portion which protrudes toward and is embedded in the elastic body such that the elastic body is bonded to the protruding portion. In this form of the invention, the provision of the protruding portion in the elastic body effectively restricts an irregular deformation of the elastic body, so that the vibration damping device of the present form of the invention can exhibit a desired vibration damping effect based on the elastic characteristics of the elastic body, with high stability. Further, the provision of the axially protruding portion integrally formed with the first mounting member permits that the first and second mounting members are opposed to each other over an increased area where the first and second mounting members are directly connected to each other by the elastic body interposed therebetween.
According to a further preferred form of the invention, the elastic body includes a first and a second axial portion located radially inwardly of the constricted part and the cylindrical portion of the second mounting member, respectively, the first and second axial portions having respective axial lengths: L and M, as measured in a cylindrical cross section taken along a cylindrical plane tangent to a radially inner end portion of the constricted part, which axial lengths: L and M satisfy the following inequality: 0.5xe2x89xa6M/Lxe2x89xa63.0.
In the present form of the invention, the first and second axial portions of the elastic body are suitably dimensioned so as to satisfy the above-indicated inequality. This arrangement makes it possible that the vibration damping device more effectively achieves both of the improved durability of the elastic body owing to the provision of the constricted part, and the sufficient volume and effective free length of the elastic body owing to the provision of the cylindrical portion of the second mounting member and the resultant high degree of freedom in determining a material of or a damping characteristic of the vibration damping device. More preferably, the axial lengths: L and M of the first and second axial portions of the elastic body are arranged to satisfy the following inequality: 1.0xe2x89xa6M/Lxe2x89xa62.0.
According to a yet further preferred form of the invention, the constricted part of the second mounting member has an inner circumferential surface which entirely comprises an inclined or a curved surface extending in the axial direction of the second mounting member, and which comprises no plane surface extending in a direction perpendicular to the axial direction. This arrangement is effective to avoid an undesirable increase of the diameter of the second mounting member due to the presence of the plane surface extending in the direction perpendicular to the axial direction, and undesirable increase of an inactive region of the elastic body where the elastic body is not deformed upon application of the vibrational load between the first and second mounting members. Thus, the present form of the invention permits a reduction in size of the vibration damping device and an improved damping characteristic of the vibration damping device, more effectively.
Preferably, the constricted part and an intersection of the constricted part with the cylindrical portion of the second mounting member axially extends over axial lengths thereof with a continuously curved inner circumferential surface having no bending portion. This arrangement effectively eliminates or reduces occurrence of stress-concentration on a local portion of the elastic body bonded to the inner circumferential surface of the constricted part of the second mounting member. In this respect, the bending portion is interpreted as an intersection of two surfaces at which there are no common lines tangents to these two surfaces.
According to a still further preferred form of the invention, the vibration damping device further comprises a fluid chamber formed in an interior space of the cylindrical portion of the second mounting member, the fluid chamber being partially defined by the elastic body and being filled with a non-compressible fluid. In this form of the present invention, the vibration damping device exhibits further improved vibration damping effect based on a resonance or flow of the fluid of the non-compressible fluid filling the fluid chamber. Further, the fluid chamber can be formed with ease, by effectively utilizing an interior space of the cylindrical portion of the second mounting member, and by closing the open end of the cylindrical portion of the second mounting member with the elastic body.
According to a yet another preferred form of the invention the vibration damping device further comprises a bracket member which is attachable to one of the two members of the vibration system for attaching the second mounting member to the one member of the vibration system, the bracket member including a fixing bore, and the second mounting member being fixed in the fixing bore such that the second mounting member is axially press-fitted in the fixing bore on the side of the constricted part thereof. In this form of the invention, since the constricted part of the second mounting member is dimensioned to have the maximum outer diameter not larger than that of the cylindrical portion of the second mounting member, the second mounting member is easily assembled in the fixing bore of the bracket by press-fitting the second mounting member from its constricted part. Further, the constricted part is provided only in the axially open end portion of the second mounting member, so that the cylindrical portion of the second mounting member effectively provides a sufficient area required for effectively press-fitting the second mounting member in the fixing bore of the bracket. For avoiding undesirable deformation of the constricted part during operation of press-fitting the second mounting member in the fixing bore of the bracket, the constricted part of the second mounting member is preferably dimensioned so as to have the maximum outer diameter (e.g., an outer diameter of the upper open end of the constricted part) which is slightly smaller than the outer diameter of the cylindrical portion of the second mounting member.
According to still another preferred form of the invention, the vibration damping device further comprises: a calking portion which is integrally formed in the other one of axially opposite ends of the cylindrical portion of the second mounting member, which is opposite to the constricted portion of the second mounting member in the axial direction, the calking portion having a diameter larger than that of the cylindrical portion of the second mounting member; and a closure member which is fixed at an peripheral portion thereof to the calking portion by calking so as to fluid tightly close the other open end portion of the cylindrical portion of the second mounting member, thereby forming in an interior space of the cylindrical portion a fluid chamber partially defined by the elastic body and filled with a non-compressible fluid, the second mounting member being positioned with respect to the bracket member in the axial direction thereof such that the calking portion is held in abutting contact with an open end face of the fixing bore of the bracket member. This arrangement permits an effective formation of the fluid chamber in the interior space of the cylindrical portion of the second mounting member, and a high-precise positioning of the second mounting member with respect to the bracket member, by efficiently utilizing the calking portion integrally formed in the other of axially opposite ends of the cylindrical portion of the second mounting member.